Lightning, just like everything, can be explored with a physics explanation. Lighting is primarily cased by the electrostatic build up in clouds. Its turns out that the bottom of the cloud ends up becoming negatively charged when lighting occurs. The explanation of why this occur is still somewhat unknown to modern science. Once the bottom of the cloud becomes very negatively charged, electrons seek the nearest positively charged object. This ends up being the ground. The electrons of the bottom of the cloud move down to the ground, and form what we see as large streaks of lighting. The reason lighting may strike a tree is that when one area of the ground is closer to the clouds than the est of the ground, it causes the electrical field to be concentrated in that one area. Even something like lighting has a practical physics explanation.